Field of the Invention
The present invention relates to a cooling system for a vehicle, and more particularly, to a cooling system for a vehicle capable of rapidly warming-up an engine upon performing a cold start-up using an exhaust heat recovery apparatus, improving fuel efficiency by upwardly controlling a temperature of a cooling water within an endurance limit of the engine depending on a driving condition of the vehicle, and improving durability of the engine, and a controlling method thereof.
Description of Related Art
Due to a global carbon dioxide (CO2) regulation and fuel efficiency regulation, fuel efficiency improvement and an environment-friendly feature have been the core issues in developing a vehicle. Advanced vehicle makers have been concentrated on development of technologies for decreasing fuel to accomplish the above-mentioned objects.
In a cold start-up condition upon initially starting the vehicle, an engine has bad fuel efficiency as compared to a condition in which it is sufficiently warmed-up. The reason is that the engine has high friction due to oil having high viscosity in a state in which a temperature of oil is low upon performing cold starting-up, and a wall surface of a cylinder has a low temperature, resulting in large heat loss into the wall surface and degraded combustion stability.
Therefore, to improve fuel efficiency of the vehicle and improve durability of the engine, it is required to rapidly increase the temperature of the engine to a normal temperature at a time of an initial start.
FIG. 1 schematically shows a cooling system according to the related art, wherein a water pump is mounted in an engine entrance in a cooling water exit controlling scheme. A portion of the cooling water which is introduced into the engine through the water pump flows to an oil cooler (also flows to LP-EGR cooler when using LP-EGR) and passes through a block and a head.
During a closing time of a thermostat (from before warm-up to less than 88° C.), the cooling water flows from a front end of the thermostat to the Exhaust Gas Recirculation (EGR) cooler and a heater cooler. In addition, after opening the thermostat (after warming-up, from 88° C. or more), the temperature of cooling water of the entire system is controlled to be cooled while the cooling water flows to a radiator.
However, according to the above-mentioned cooling flow passage configuration, since the cooling water flows in all fluid passages except for the radiator before the warming-up, heat generated from the engine is dispersed, thereby causing interruption for a rapid increase in the temperature of the engine, and about 30% of energy generated during a combustion process may be lost through exhaust gas.
In addition, since the thermostat (of a wax type) is opened or closed only in a physically set temperature range, it has no choice but to control the temperature of the entire cooling system at a predetermined temperature regardless of a driving condition and it is difficult to manage heat loss and engine friction.
The information disclosed in this Background of the Invention section is only for enhancement of understanding of the general background of the invention and should not be taken as an acknowledgement or any form of suggestion that this information forms the prior art already known to a person skilled in the art.